1. Field of the Invention
The present invention relates generally to slide fasteners and more particularly to slide fasteners of the type having a series of discrete fastener elements made of a synthetic resin secured to each of a pair of oppositely disposed stringer tapes.
Still more specifically, this invention deals with a slide fastener of the type described which incorporates an improvement in the fastener elements whereby the elements once coupled together are retained in place against displacement relative to each other particularly in a direction perpendicular to the plane of the slide fastener when the latter is subjected to longitudinal or lateral bending stresses, or torsional stresses while in use.
2. Prior Art
In one such prior art slide fastener, each individual fastener element was provided at the front end of its coupling portion with a horizontally extending, elongate slot or recess for receiving corresponding projections formed on a mating fastener element when the two stringer tapes are taken into engagement with each other.
Another prior art fastener element included a pair of slots formed in opposite sides of the coupling end portion and extending along the length of each fastener element.
A common drawback of these known slide fasteners is that when severe bending or torsional stresses are applied to the stringer tapes, the pronjections received in the corresponding slot are susceptible to accidental separation from the latter, resulting in a malfunctioned slide fastener.
This difficulty arises out of the fact that the mechanical strength of the fastener element is considerably reduced at its coupling portion on account of the provision of such continuous slots which tend to be deformed in the direction of the thickness of the coupling end portion under the influence of increased bending or torsional stresses.